With current perpendicular magnetic recording technology, the magnetic recording areal density has reached around 700 to 800 Gb/in2, which is reaching the physical upper limit due to the superparamagnetic effect. In hard disk drives, the superparamagnetic effect sets a limit on the storage density due to the minimum size of magnetic domain that can be used in a magnetic recording medium. Although magnetic materials with higher coercivity such as FePt, CoPd, etc. are available, these materials generally have poor writability as a result of insufficiencies in the writing field of conventional writing heads.
Energy assisted magnetic recording (EAMR) or heat assisted magnetic recording (HAMR) technology has become the common pursuit in the field of data storage art because it is one of the most promising solutions to circumvent the above described writability problem and further push the data areal density to 1 Tbit/in2 and beyond.
In an EAMR system, a light coupler, a waveguide, and a near-field transducer (NFT) are generally inserted between a reader and a writer. The light that is coupled from an integrated or an attached external light source propagates along the waveguide and focuses on a small area close to the air bearing surface (ABS) of a slider where the NFT is located, and in the neighborhood of the waveguide. The NFT is a strong absorber of light waves at resonant status assisted by a surface plasmon effect. Therefore, the NFT is capable of squeezing or concentrating the light energy to a very tiny area (e.g., 40 nm) and acts as a relay to deliver the concentrated energy to the recording layer of a recording medium, which is positioned only several nanometers away within the near-field zone of the NFT. With the concentrated light energy, the recording medium can be temporarily heated up and becomes magnetically soft such that a writing magnetic field can flip the magnetic direction of the medium in the heated area to store the desired bit data.
In the EAMR system, the NFT absorption at resonant status is very strong, and the generated heat is confined within a very tiny region. Therefore, the temperature of the NFT can be very high and can even be higher than the melting point of the NFT material. That can lead to non-reversible plastic deformation of the NFT, and portions of the NFT material may be pushed outward, resulting in burnishing. Eventually, both the NFT and the recording medium can be damaged. Therefore, it is important to prevent the temperature of the NFT from increasing too high and to prevent potential NFT and/or recording medium damage. The conventional method is to equip the EAMR head with a metal heatsink or chimney made of a material having relatively high thermal conductivity such as Au, Cu, Al, etc.
Although the metal heatsink can help to prolong the lifetime of the NFT to some extent, the metal heatsink still has several drawbacks. First, the metal heatsink generally provides a relatively narrow heat channel to carry the heat accumulated in the NFT away through a writing pole. Nevertheless, the writing pole itself also absorbs light energy from an adjacent waveguide and forms an additional undesirable heat source. Furthermore, the writing pole itself is not a very good heat conductor.
Second, the metal heatsink generally cannot be larger than the NFT, otherwise the NFT performance will deteriorate substantially. Therefore, the heat capacity of the metal heatsink itself is quite limited. Third, there is a significant risk of damaging the NFT during the process of fabricating the metal heatsink because it is smaller than the NFT. In order to avoid damaging the NFT, additional stop layer(s) (e.g., Cr, Ni, Ra, etc.) are often added between the NFT and the heatsink during fabrication of the EAMR head. However, the existence of the stop layers has a considerable negative impact to the optical performance of the NFT, and the thermal performance of the stop layers can be even worse than the metal heatsink since these materials are very absorptive. In the related art, the metal heatsink typically will naturally form a conical shape that results in a smaller contact area of contact between the NFT and the metal heatsink. As such, the heat dissipation rate will be poor. Therefore, it is desirable to provide an EAMR head with improved heatsink performance for EAMR applications.